In October 2006, the Maison des sciences de l'homme et de l'environnement Claude Nicolas Ledoux (Besançon) brought together some twenty French and foreign researchers from a wide range of disciplines - architecture, history, art history, philosophy and anthropology - at the Saline Royale d'Arc-et-Senans to commemorate the bicentenary of Ledoux's death by examining the significance, challenges and future of his work. Ledoux was an architect who left behind a number of famous works, including the UNESCO World Heritage-listed Saline, but he was also the author of an often enigmatic book on architecture, the strangeness of which specialists continue to question. His work, both written and built, raises a number of questions relating to the history of architecture, the development of utopian currents and the regenerative project of the Enlightenment. The volume is divided into three parts. The first brings together studies devoted to Ledoux himself, both as a writer and an architect. The second attempts to place Ledoux in his context by studying influences, competition and legacies. Finally, the third extends the focus to ideal cities by examining the exchanges between architecture and utopia.